Method and means for making elbows by forcing tubular stock through a die



2,831,523 ING April 1958 P. D. WURZBURGER METHOD AND MEANS FOR MAKINGELBOWS BY FORC TUBULAR sTocx THROUGH A DIE Filed May 20, 1955 3Sheets-Sheet 1 INVENTOR.

P 22, 1958 P. D. WURZBURGER 2,831,523

METHOD AND MEANS FOR MAKING ELBOWS BY FORCING TUBULAR STOCK THROUGH ADIE Filed May 20, 1955 Y 3 Sheets-Sheet 2 D //R D I V/B 20 a H ,2! l0 l5a F 7 8 INVENTOR.

April 1958 P. D. WURZBURGER 2,831,523

ws'mon AND MEANS FOR MAKING ELBOWS BY FORCING v TUBULAR s'rocx THROUGH ADIE Filed May 20, 1955 5 Sheets-Sheet 3 g INVENTOR. Pom 0 Wuezaweaze. BY

6 ,l/farne A United States Patent METHOD AND MEANS FOR MAKmG ELBOWS BYFORClNG TUBULAR STDCK THROUGH A DIE Paul D. Wurzburger, ClevelandHeights, Ohio, assignor to Nibco, Inc, Elkhart, End, a corporation ofIndiana Application April 12, 1951, Serial No. 220,632, new Patout No.2,715,432, dated August 16, 1955, which is a continuation of abandonedapplication Serial No. 611,600, August 20, 1945. Divided and thisapplication May 20, 1955, Serial No. 509,732

6 Claims. (Cl. 153-48) This invention relates to a metal working and toa method of making tubular elbows and elbow fittings and moreparticularly, to a method of making short radius wrought elbows.

This application is a division of my prior copending application SerialNo. 220,632, filed April 12, 1951, now Patent No. 2,715,432, grantedAugust 16, 1955, which application is a continuation of my abandonedapplication, Serial No. 611,600, filed August 20, 1945. v In the art towhich my invention pertains it has been known to make elbows ofrelatively large radius by merely forcing a tubular blank withoutinternal support through the curved channel of a forming die. Suchmethods are limited in their use and application at the point wherewrinkling and undesirable deformation of the metal begins to occur asthe radius of curvature, in relation to, inter alia, the diameter of thedesired elbow, is decreased. Having in mind the variations resultingfrom the use of different metals and the different relations of wallthickness to tube diameter, it may be taken as a general propositionthat undesirable wrinkling limits this prior art method to makingwrought 90-degree elbows or bends having a minimum radius of curvature,as measured on the external surface at the inner bend, about equal tothe outside diameter of the tube.

When in the prior art it has been desired to make elbows of shorter orsmaller radii in relation to diameter the teaching of the prior art hasbeen to give the tube or blank internal support whereby to maintain itsinternal diameter at or substantially at its desired finished internaldiameter whilst the blank is being bent as by movement through theangled channel of a forming die. Such in ternal support has beenprovided in filling the blank with more or less plastic or liquidmaterial such as lead, sand, resin, tar or water and/or by causingsizing balls to move within the blank or piece whilst the blank is beingbent. Others in the prior art have provided internal support for theextruded leg or posterior portion of the blank through supportingmandrels whereby to resist the tendency of the material to collapseinwardly upon being forced to take the small radius turn.

In the methods where internal support has been provided to resist thetendency of the walls of the blank or elbow to collapse inwardly or towrinkle, there have been concomitant limitations, namely that resistanceto the formation of wrinkles has built up, oft-times greatly orexcessively, an increased resistance to forcing the work around thecorner or bend of the forming channel. The eifect of the internalsupport which requires the greater force to move the blank through thedie is not limited merely to requiring greater working efforts to bringabout the formation of the elbow but along with the greater workingeffort follows the greater stress and working of the metal of the blankas well as a tendency to thicken certain wall portions and/or thin outother portions and to expand the walls whereby to increase thefrictional load between the outer surface of the blank and the channelof the die. These difliculties increase as the ratio of the radius ofcurvature to the diameter of the elbow is reduced so that the methodswhich rest upon internal support for the blank during the forming of thebend run.

terial of the elbow of necessity bring about reductions in.

the speed of production and increases in cost as well as many practicaldifliculties inherent in the very nature of the internal supportingmeans or mechanisms such as balls, articulated mandrels or in otherinstrumentalities.

It is among the objects of my invention to provide an improved method offorming elbow fittings which seeks to avoid the various difiicultiesdiscussed above by,a simple process which is economical from theproduction point of view, yet practicable and satisfactory in operation. A more specific object of my invention is to provide a method offorming short radius elbow fittings of high and uniform strength,utility and quality. By

short radius I have in mind that the ratio of the radius of the externalsurface of the inside corner of the elbow to the outside diameterthereof be less than unity, and preferably a small fraction of unitysuch as about onethird to one-quarter.

Another object of my invention is to produce a method of making shortradius elbows in which the walls of the blank and elbow aresubstantially relieved of deleterious stresses and strains during theformation of the bend thereof and more particularly, during theformation of the bend in the elbow during the step of forcing the blankthrough an elbowed channel of a forming die.

Another object of my invention is to preserve a substantially uniformwall thickness in and throughout the parts of the elbow formed accordingto my invention. Another object of my invention is to provide a methodof forming elbows which can be carried out with the expenditure oflittle or a minimum of power for forcing the blank through the dieand/or working the material from an initial straight tubular form to afinished short radius elbow form. Another object of my invention is tosubstantially eliminate spring back in the elbow after the same isremoved from the forming die or mechanism. A primary object of myinvention is to provide a meth 0d of forming commercially useful rightangled elbows or elbow fittings having such a small ratio of radius ofcurva ture to diameter that upon their being subjected to bending as bybeing forced through a forming die without into wrinkle and have otherdeformations from its ultimately desired shape. Another and morespecific objectof my invention is to provide a method for forming shortradius elbows in which resistance to the formation of the bend of theelbow as by forcing a tubular blank through a ring angled channel of aforming die is maintained at a low value by the complete, substantial orpartial elimination of internal support for the walls of the material ator adjacent the bend of the elbow while the same is being formed.

Other objects and advantages of my invention will appear from thefollowing description of preferred. and modified forms thereof,reference being bad to the accompanying drawings in which:

Figure 1 shows in longitudinal cross-section a tubular blank positionedin an initial position in one of ;a pair 7 Figure 2 is a view similar toFigure 1 showing the Patented Apr. 22, 1958,

blank in cross-section in an advanced position in its movement in thechannel of the forming dies.

Figure 3 is a view similar to Figure l showing the blank in fullyadvanced position at substantially the end of the formingstroke.

Figure 4 is a top plan view of the partially formed elbow in thecondition shown in Figure 3.

Figure 5 is an end elevation of the same partially formed elbow shown inFigures 4 and 3.

Figure 6 is a view taken partially in the plane of the split of theforming dies showing the partially finished elbow in the position ofFigure 3 preliminary to the entrance of an ironing mandrel.

Figure 7 is a view similar to Figure 6 in respect to the forming diesand the parts contained therein and associated therewith showing theironing mandrel in advanced position.

Figure 8 is a view similar to Figure 7-showingan ironing mandrel in aretracted position following the step depicted in Figure 7.

Figure 9 is a view of a modified procedure and apparatus, the view beingsimilar to that of Figure 1 and comprising a section taking in the planeof the split of the forming dies with the blank in its initial preformedposition and with a modified form of ironing mandrel in place.

Figure 10 is a view similar to Figure 9 showing the blank in theposition advanced from that shown in Figure 9.

Figure 11 is a view similar to Figure 10 showing the blank in its mostadvanced position preliminary'to movement or withdrawal of the ironingmandrel.

Figure 12 is a view similar to Figure 11 showing the ironing mandrel inits withdrawn position after the same has ironed out the wrinkles fromthe extruded leg of the elbow.

Figures l3, l4, l5 and 16 are respectively transverse sectional views ofthe ironing mandrel shown in Figures 9 to 12 inclusive, taken along thelines 1313, 1414, 1515, and 16-16 of the ironing mandrel of Figure 12.

To accomplish the objects and advantages of my invention I place atubular blank of malleable and ductile material to be formed into theelbow in the channel of a forming die which has a short radius elbowedform substantially corresponding to the external form of the finishedelbow. Then preferably without substantially supporting the blankinteriorly I cause to be exerted a longitudinal force on the trailingedge of blank remote from the bend of the elbow and thereby forciblyadvance the blank through the bend of the channel of the die to give theelbow its angled form while permitting the material of the leading endof the blank to become wrinkled and deformed, but not excessively so, asit passes through and beyond the bend of the forming channel. I havefound that at the completion of this stepof the forming operation thatthe trailing leg and the bend of the partially formed elbow, see Figures3, 4 and 5, are not only not deleteriously deformed but are in factsubstantially superior in conformation, size, internal stress, wallthickness, contour and the like to similar parts formed by prior artmethods in which effort has been made to provide internal support forthose parts of the blank which tend to collapse or wrinkle while theblank is being forced through the angled channel of the die.Substantially all the wrinkling and deformation of the whole blank isconcentrated in the leading, i. e., extruded leg of the piece, butsince'this leg has been free from internal support and has beenpermitted to take its own shape it has not been unduly stressed nor hasit caused undue stresses, thickening or thinning out of other parts ofthe piece. After the piece has been given its initial elbow form, albeitwith an imperfect leading leg, I thereafter, by means presently to bedescribed, remove the imperfections from the leading leg and have for myproduct a short radius elbow small diameters and/or thick walls.

'4 with the desirable characteristics sought and mentioned above.

I have found my method to be practicable and advantageous when practicedwith such malleable and ductile metals as hard or soft copper, lowcarbon steel, stainless steel and aluminum alloys as are commonlyemployed in commercial tubular stock. Without trying to state all thedifferent kinds of metals or the range of sizes or relations of wallthickness to diameter in dilferent materials with which my method may beadvantageously practiced, my observations have been that while tubes orblanks or excessively soft metals and/ or large diameters and/ or thinwalls require less effort to bend, the apparent advantage may tend to bemore than offset when some or all of these characteristics admit ofexcessive thickening, wrinking or other undesirable effects in the workpiece. The converse follows with excessively hard materials,

Having these limitations in mind I have provided, as will more fullyappear below, precautionary steps for controlling wrinkling, forexample, in the leading leg of the elbow whereby to extend the usefulrange of my invention against the apparent limitations mentioned above.The following descriptions and illustrations of preferred and modifiedforms of my invention are based especially on tests and demonstrationsemploying one-half inch 0. D. copper tube, soft temper, with 0.035 wallthickness; the finished elbow turning at degrees about a one-eight inchinside radius of curvature.

A preferred form of carrying out the method according to my invention isillustrated in Figures 1 to 8 inclusive. In all these figures except 4and 5, Ive illustrated diagrammatically the half die D of a split pairof forming dies, the parting plane of which is in the plane of thedrawings. Such die halves are opened in the known way to receive theblank, or piece, closed to form the forming channel of circularcross-section (the half channel C being shown in the half die D), heldclosed during the forming operation and finally opened to permit removalof the piece after it has been formed. The channel C has a straightcylindrical entering section 1 long enough to receive the tubular blankor work piece B, a bend 2 with inside radius r and diameter d, thelatter being equal to the diameter of the entering section 1, and thestraight cylindrical forming section 2, the latter having its axis asshown at 90 degrees to the axis of the entering section 1. As shown inFigure l, the blank B is preferably of the right cylindrical form withsubstantially square ends and preferably has an external diametersubstantially equal to the internal diameter d of the channel C. A powerdriven ram R enters the upper (as viewed) end of the section 1 of thechannel C with its shoulder S engaging the end of the piece B and itspilot P entering and closely fitting the trailing end of'the piece. InFigure l the ram R is in position preliminary to exerting the force,downwardly as viewed in Figure 1, whereby to urge the blank around thebend 2 of the channel of the die. The pilot P may be as long as thetrailing leg of the finished elbow.

With the blank B positioned in the die D as shown in Figure 1, andwithout internal support for or engagement of the blank other than bythe ram R and the interior surface after channel C, downward movement ofthe ram forces the leading end of the blank into the bend 2 of thechannel C as shown in the midst of its travel in Figure 2. Here it willbe observed that the inner leading edge 10 of the blank tends tocontinue ina straight line rather than to turn the corner whereas theouter leading edge 11 of the blank is being forced around the curvedouter wall of the channel C and has substantially swung through an arcof about 90 degrees. As will also be observed in Figure 2, the wall ofthe blank adjacent the outer curve of the bend 2 has spaced itself alittle away therefrom whilst the open leading end 12 of the blank hastaken an irregular form incident to thetpermissive deformation thattakes place during the travel of the work from the position shown inFigure l to that of Figure 3. The view of Figure 2 is intended toillustrate the position of the parts at the instant of their continuousmovement through this stage of the advance of the blank through thechannel of the forming die. Further continued movement 2 of the ram fromthe positions shown in Figures 1 and 2 bringsv the parts to the positionshown in Figure 3 and thus to the end of its forming step. At the end ofthe stroke of the ram R, as shown in Figure 3, it will be observed thatthe elbowed piece has been given its general configuration with theleading inner edge 14) as well as the outer wall of the bend of theblank returned to contact with the wall of the channel C and the outerleading edge 11 of the blank has come out of contact with the adjacentwall of the channel. The open leading end 12 has taken a somewhatdifferent form from that shown in Figure 2, and the upper surface of theextruded leg contains deep though smoothly formed wrinkles 13 and 14,see also Figures 4 and 5 wherein the elbowed piece B is shown in full asit would appear if removed from the dies after having been worked to thestate of Figure 3. In this stage of the formation of the elbow it willbe observed that while the inner wall of the elbow has tended to thickena little at the corner that the outer wall 16, particularly at the bend,has not been weakened or materially reduced in thickness. Moreover, ithas been my observation that freedom from internal support andsubstantial interference with the natural bending and working of themetal has permitted the various parts of the piece to flowlongitudinally and circtunferentially relative to each other withrelative freedom whereby to accommodate themselves to the change in formof the piece Without requiring excessive (wall thickening) pressure fromthe ram and without fracture of or creating deleterious internalstresses within the piece.

Preferably, the work piece B is not removed from the dies after theabove step as shown in Figure 3, is completed but rather the working ofthe piece is continued as shown in Figures 6 and 7. In Figure 6 the workpiece and the ram R are shown in the same condition as in Figure 3. inFigure 6, however, there is shown in the left of the figure a second ramor ironing mandrel M connected with and actuated by such means as ahydraulic cylinder H whereby to give the mandrel M a rightward andleftward movement, as viewed in Figures 6, 7 and 8, under appropriatecontrols, not shown, to carry out the second step of my method about tobe described. The mandrel M has a rounded nose and enters the section 3of the channel C of the dies D and the open leading end 12 of the workpiece to expand the same as well as expand and iron out the wrinkles 13and 1 5, to form the intended finished internal and external diametersof the extruded leg of the piece. Preferably, the mandrel M enters thechannel C through a guiding sleeve 21 which has substantially thefinished wall thickness of the work piece so that the mandrel is guidedin axial alignment with the finished wall thickness desired to be formedin the leading leg of the work piece. Forcible movement of the ironingmandrel M from left to right as viewed in the drawings advances themandrel from the position shown in Figure 6 to the position shown inFigure 7 whereby it will be seen that the wall of the leading leg of theelbowed piece has been brought back to substantially cylindrical form,eliminating the wrinkle 13 and 14 and opening the open leading end 12 ofthe elbow to substantially true right cylindrical configuration. Whilethe ironing mandrel M is forcibly advanced from the position shown inFigure 6 to the position shown in Figure 7 the ram R is held in its mostadvanced position as shown in Figures 3-7 whereby to resist the tendencyof the piece to be moved backward in the channel by the entering strokeof the mandrel M. During the inward and ironing stroke of the mandrel Mnot only is the wall of the leading leg of the piece expanded radiallyand brought to a more uniform Wall thickness but also is the thicknessand fullness of the 6 outer bend 16 of the elbowed piece enhancedwhereby to eliminate the tendency of the elbow to spring or springbackto a somewhat different form than the angled form of the channel of thedie.

After the mandrel M has been advanced to substantially its point ofmaximum penetration as shown in Figure 7, it is then forcibly withdrawnfrom the leading leg of the elbow, see Figure 8, its movement during itswithdrawal adding to the burnish of the interior of the leg of the elbowand perfecting the desired form and finish thereof. Preferably, the ramR is Withdrawn from engagement with the trailing end of the elbow afterthe ironing mandrel M has passed from contact with the lead-.

ing leg thereof, see Figure 8. My method may be advantageously practicedeither by direct manual control of the movements of the ram and mandrelor by appropriately correlated automatic or'semi-automatic mechanismsand controls which can be adjusted to the practice and known andpracticed in the art before my invention, the

respective ends of the elbowed piece may be treated by way ofenlargement or other trimming or sizing to form appropriate sockets toreceive tubes in capillary or other bonded joints or otherwise treatedappropriately for thepurposes to which the elbows are intended to beused.

The obliqueness of the leading end of the elbows as shown at 12 inFigure 8 is a thing which I have found to be substantially insignificantin respect to the essential steps of my process and the final finishingor sizing of the product, particularly with the materials which I haveemployed as mentioned above and in the so-called smaller sizes ofelbows, i. e., about 1 or less outside diameter. In the event that theobliqueness of the leading end of the elbowed piece in "thesemi-finished form shown in Figure 8 takes on a deleterious significancein point of the final sizing, finishing or truing operations to beperformed after the novel steps of my instant method are performed, thenI find that I can substantially control the obliqueness of the opening12' by cutting the end of the blank a little on the bias rather thantruly in the right cylindrical form as shown in Figure 1. Where theblanks are cut on the bias I place them in the die so that the longerwall will be the outside wall of the bend of the elbow with theresult'that in the piece as shown in Figure 8 the outer leading edge 11will lie more nearly directly opposite the outer leading edge 10.Otherwise, I prefer to use blanks with right angled ends since no careneed be taken with respect to the position of the blank around its ownaxis in the dies.

Referring to Figures 9 through 16 a modified form of my method will nowbe described. Here, as shown in Figures 9 to 12 inclusive, I prefer toemploy the same dies D, having the same forming channel C which in turnhas the same entering section 1, bend 2 and forming section 3 allsubstantially identical in the structure and function as first abovedescribed. Here also, I may employ the same ram R with the shoulder Sand pilot P, the action and function of which may be the same orsubstantially as above described. As shownin Figure 9, the blank tubularWork piece B may be the same as the piece B shown and described inFigure 1 and may fit the channel C of the die and be advanced therein bythe ram R into and through the bend of the channel by the same movementof the ram R as above described.

In this modified form of my invention, however, I employ a differentform of ironing mandrel N, see also Figures 13 to 16, and operate themandrel N in a specifically different way from that in which the mandrelM is operated. As shown in Figure 9, the mandrel N has the whole of itsworking end 30 lying within the forming section 3 of the channel C withits head part 31 lying within the bend 2 of the channel. I prefer thatthecylindrical shank portion 32 of the mandrel N slide with a snugsliding fit within a guide sleeve or tube 33 which preferably hassubstantially the same wall thickness as the ultimately desired wallthickness of the leading leg of the elbow whereby to guide the mandrel Naxially in its movement Within the channel and to support the lower sideof the mandrel especially during the latter part of its ironing strokeas will be more fully described below. The mandrel N like the ram R andmandrel M is actuated by appropriate actuating means such as a hydrauliccylinder or otherwise whereby to give forceful rightward and leftwardmovement as viewed in the drawings in alignment with the axis of theforming section 3 of the channel C. The pilot sleeve 33 may also beappropriately actuated by power means not shown, whereby the end of thesleeve 33 may be disposed as much as little within the section 3 of thechannel as may be desired in relation to the leading end or open end ofthe extruded leg of the elbow.

As shown with particular reference to Figures 13 to 16, the working end30 of the mandrel N departs from the cylindrical form of the shank 32thereof by a tapering relief cut away from the upper side of the mandrelas viewed in these figures, whilst the lower part of the working end ofthe mandrel retains a substantially semi-cylindrical cross-section fromthe end of the shank portion 32 up to the head portion 31 thereof. Asshown more particularly in Figure 15, the top surface of the head 31 issubstantially semi-cylindrical lying in a projection of the top surfaceof the shank 32. This semi-cylindrical surface extends approximatelybetween the points 34 and 35 rightwardly and leftwardly, as viewed inFigure 9, and merges leftwardly, into a rounded upper surface whichmerges smoothly with the upper relief of the working part 30 of themandrel at and about the point and corner 36. The forward and downwardface of the head 31, comprising the surface opposite the outer bend 2 ofthe channel, is similar to the adjacent surface of the bend and thussubstantially spherically formed whereby to be spaced from the outerbend of the channel approximately the thickness of the wall of theblank. As shown in Figure 9, it will appear conversely that the point 36at the place of maximum relief is most widely spaced from the innercorner of the bend 2 of the channel whereby to permit the inner leadingedge of the blank B to pass with desired freedom beyond the inner turnof the channel without substantially contacting or without excessiveforceful bearing upon the mandrel N as the blank is advanced through theforming die, see Figure 10.

In this'form of my invention while I do not entirely avoid all interiorsupport or contact for the blank as it F is advanced in the forming die,I have found that a mandrel shaped substantially like the mandrel N withthe greater relief on its upper face, i. e., its face adjacent to andfacing the inner turn of the channel, exerts little enough force orfriction upon the inner surfaces of the blank as the latter is forcedthrough the channel as to preserve substantially the advantages of thecomplete absence of internal support for the blank during the bendingoperation. Thus, when the ram R begins its stroke, downwardly as viewedin the drawing, forcing the blank along the section 1 of the channel andinto and through the bend 2 thereof and in part into the section 3 ofthe channel, the leading end-of the blank encompasses and in the mainslides freely past the head of the mandrel N as well as substantiallyall of the working end 30 thereof with much the same facility ofmovement that the blank has in the first step described with referenceto Figures 2 and 3 above. As shown in Figure 10, the outer leading edge11 of the blank passes between the smooth outer and lower surface of thehead 31 of the mandrel whilst the inner leading edge 10 of the blank isbent away to the left as viewed in Figure 10, under the influence of themovement of the body of the blank and the curvilinear movement of theouter leading edge 11 and adjacent parts. Continued movement of theblank B' beyond the position shown in Figure 10 and approaching theposition shown'in Figure 11 may induce the inner leading edge 10 of theblank to contact more or less the upper relieved face of the working endof the mandrel more or less forcibly but with much less than harmfulresistance to the movement of the blank through the forming channel. Atthe end of the forming stroke of the ram R the blank B will have beengiven its elbowed form and the leading leg of the blank will havesubstantially encompassed the working end 30 and the mandrel N as shownin Figure 11. The inner wall of the leading leg of the elbow will bewrinkled as at 13' and 14' substantially corresponding to the wrinkles13 and 14 above described, and the open leading end 12 of the piecewill, have a configuration more nearly corresponding to the end 12 asshown in Figure 8, than the end 12 as shown in Figures 3, 4 and 5 above.It will also be noted in this form of my method that the outer wall ofthe bend of the elbow has been maintained in substantial contactthroughout the whole of this forming step with the lower and outerWorking face of the head of the mandrel.

The elbowed blank, however, as shown in Figure 11 has been given itselbowed form with great freedom of the parts of the leading leg towrinkle and take paths of longitudinal, curvilinear and circumferentialmovement with respect to the other parts and the axis of the leading legwhereby to be relatively free of deleterious stresses or tendencies tofracture, and similarly the ram R has not been called upon to deliverexcessive forces to advance the blank longitudinally around the bend ofthe channel. Such little resistance as the mandrel N has offered to themovement of the blank B' will have tended in some measure to cause theinner wall 15 to be somewhat thicker than the inner wall 15, Figure 3,of the elbowed blank B and correspondingly, the outer Wall 16' of theelbowed blank as shown in Figure 11 may well tend to be a little thickerthan the outer wall 16 of the blank B under the circumstances shown inFigure 3. Following my fundamental teachings, however, it remains inthis modified form, as it did in the preferred form, to iron out orsmooth out the wrinkles and other deformations particularly in theextruded leg of the elbowed blank. Peculiarly, advantageous to theinstant form of my method is the position of the ironing mandrel N, asshown in Figure 11, interiorly of the elbowed blank so that forciblewithdrawal of the mandrel N will by virtue of its form and contour abovedescribed iron out and give the desired cylindrical contour to theleading leg of the elbowed blank. Leftward movement of the mandrel N, asviewed in Figures 11 and 12, will bring the upper semi-cylindricalsurface of the head 31 with its rounded shoulder at 34 into ironingcontact with the wrinkled and deformed inner wall 15' of the leading legof the elbowed blank ironing the wrinkles out as the head of the mandrelprogresses leftwardly from the position shown in Figure 11 to theposition shown in Figure 12, and placing that portion of the wall 15adjacent the inner turn of the channel in a state of drawing tensiontending to thin the wall more or less especially adjacent the inner bendof the elbow depending upon the tightness of the fit of the head 31 inthe extruded leg of the blank B. While the mandrel N is being withdrawnand ironing out the inner wall 15 the mandrel, its working end 30 andthe head 31 are supported in proper axial position by virtue of thebearing of the whole lower semi-cylindrical portion thereof upon theouter semi-cylindrical wall 16 of the leading leg of the elbow and uponthe sleeve 33. When the mandrel N has been moved to the position shownin Figure 12 and after the ram R has been Withdrawn as described inconnection with the preceding form of my method the dies D may be openedand the elbowed blank, finished in the sense of being properly elbowed,may be removed from the dies for further sizing and finishing treatmentin the same way and for the same purposes mentioned above. Preferably,the ram R is not withthis modified form of my method by first causingthe ram R to take its whole stroke before beginning the ironing strokeof the mandrel N, I have also found it advantageous to initiate theironing stroke of the mandrel N prior to the full completion of thestroke of the ram R, i. e., the ironing stroke may begin when theramming stroke is about three-fourths completed, i. e., with thetrailing and leading ends of the blank at about the position of thedotted lines 39 as shown in Figure 11. Preferably, the ironing mandrel Nthen moves at a greater speed than the ram while both instrumentalitiesare moving and no substantial wrinkling or undesirable deformationoccurs rightwardly of the withdrawing head of the mandrel N because thegreat tendency toward wrinkling and undesirable deformation takes placein the blank more nearly adjacent the leading end thereof than in thoseportions of the blank adjacent the bend, see Figures 3, 4 and 11, andcf. Figures 2 and 10. The correlation of the movement of the mandrel Nand the ram R may be efiected by manual and visual control or byautomatic controls known in the art. Where both mandrels are sought tohave motion at the same time, at least within the latter part of theramming stroke, an automatic control to initiate the movement of theironing mandrel at a particular point of the travel of the ram will bemuch preferred if not necessary to bring about the correlations ofmovements last above described. After the parts have first arrived atthe position shown in Figure 12 the ironing mandrel N may be givenadditional reciprocatory ironing strokes while the ram R positions thepiece if that be found necessary or desirable.

The drawings and the foregoing specification constitute a description ofthe improved method and means for making elbows in such full, clear,concise and exact terms as to enable any person skilled in the art topractice the invention, the scope of which is indicated by the appendedclaims.

What I claim as my invention is:

1. The method of forming elbows from tubular stock open at both endswhich comprises forcing a tubular element endwise partly through a diestructure comprising an elongated passage of circular cross-sectionhaving first and second straight end portions and an arcuately curvedportion connecting said straight end portions and a mandrel having ahead in said arcuately curved portion to define a generally annularspace therewith and a shank in said second straight end portion, saidhead being of partly circular cross-section in planes perpendicular tothe axis of said second straight end portion and said head and shankbeing shaped to provide an enlarged space within the second straight endportion at the side thereof adjacent the center of curvature of thearcuately curved portion, and partly through the annular space betweensaid head and arcuately curved portion and partly into the enlargedspace within the second straight end portion, and thereafter withdrawingsaid mandrel through the end part of said tubular element which has beenforced beyond the annular space to smooth and straighten the end partinto conformity with the straight end portion of the die.

2. Apparatus for forming elbows from tubular open ended elementscomprising a die having an elongated passage extending therethrough,said passage consisting of two angularly related straight end portionsand a curved intermediate portion connecting said end portions, aplunger movable into one straight end portion of said passage and havinga reduced end portion dimensioned to fit within a tubular element whichin turn fits within said passage, and a shoulder en'gagea'ble with.

the end of such tubular element, a mandrel having a head adapted to belocated within the curved intermediate portion of said passage and todefine therewith an annular space, said mandrel having a reduced neckforming with the interior of the other straight" end. portion of thepassage at theside thereof adjacent thecenter vof .curvature an enlargedchamber permitting wrinkling of the wall of the tubular element at theinside of a bend therein as it is forced around the curved portion ofthe passage into the said other straight end portion, means for forcingsaid plunger into one end of said passage, means for supporting saidmandrel in the other end of said passage with said head located in thecurved intermediate portion of said passage, and for withdrawing saidmandrel fromsaid passage after said plunger has been moved into saidpassage to force a tubular element partly around said curvedintermediate portion of said passage through said annular space and intothe straight end portion of said passage in which said mandrel islocated.

3. Apparatus as defined in claim 2 in which said passage is ofsubstantially uniform circular crosssection.

4. The method of forming an elbow from tubular stock which comprisesplacing the stock in a die having an elbow shaped passage including anarcuate bend, providing a headed mandrel within the passage at said bendto define a restricted space at the outside of said bend, said mandrelhaving a curved concave surface adjacent the inside of said bend spacedsubstantially from the passage wall to provide a laterally enlargedspace into which the wall of the 'tubular stock may wrinkle, forcing thestock through the die partly past said head to extrude the materialunder pressure at the outside of the bend and to bend the material atthe inside of the bend, and thereafter withdrawing the head to shape thematerial at the inside of said bend under tension.

5. The method of forming an elbow from tubular stock which comprisesplacing the stock in a die having an elbow shaped passage including anarcuate bend the radius of curvature of which as measured on theexternal surface at the inside of the bend is not greater than one-thirdof the outside diameter of the tube, providing a headed mandrel withinthe passage at said bend to define a restricted space at the outside ofsaid bend, said mandrel having a curved concave surface adjacent theinside of said bend spaced substantially from the passage wall toprovide a laterally enlarged space into which the wall of the tubularstock may wrinkle, forcing the stock through the die partly past saidhead to extrude the material under pressure at the outside of the bendand to bend the material at the inside of the bend, and thereafterwithdrawing the head to shape the material at the inside of said bendunder tension.

6. The method of making an elbow from a thin walled metal tube whichcomprises pushing the tube by force applied to its trailing end into achannel of a circular cross-section of substantially the same diameteras the tube, the channel comprising first and second straight portionsconnected by a curved portion in which the ratio of the radius ofcurvature, measured at the inside of the curved portion, to the diameterof the channel is not substantially greater than one-third, providingsubstantial clearance within the second straight channel portion beyondthe curved portion at the side thereof adjacent the center of curvatureto permit the formation of relatively deep wave-like wrinkles bypositioning within said channel a mandrel having a head at one endthereof and a reduced neck adjacent the head, with the head of saidmandrel in the curved portion of the passage and the reduced neck of themandrel in the second straight channel portion during movement of thetube into the passage, stopping movement of the tube'while' substantialportions remain in both straight channel portions, and thereafter, whilethe tube remains in the passage, working out the wrinkles in the forwardleg of the elbow by applying outwardly acting forces from within theforward leg by withdrawing the mandrel through the second straightchannel portion.

References Cited in the file of this patent UNITED STATES PATENTS AndresMar. 8,

Frandsen Dec. 21,

Kvarnstrom Nov. 30,

FOREIGN PATENTS Germany July 14,

Great Britain June 21,

